Multicolor filter



I Feb. 1, 1938.: HEYMER 2,107,116

MULTI-COLOR FILTER Filed May 21, 1935 In van for By Afforne9s '2 I Patented Feb. 1, 1938 "PA ENT orrics arcane uouncoma mm' Gerd Heymer, Wolfen, m Bitterield, Gerascignor to Ms Ansco Corporation,

many, I Binghalnton,

Application May 21,

v In Germany My present invention relates to a multi-color filter and more particularly a multi-color filter capable of being ,obturated concentrically. It is a continuation in part of my co-pending ap- 5 plication Ser. No. 597,601, filed March 8, 1932.

One of its objects is to provide a mask allowing the concentrical obturation. Further objects will beseen from the specification following hereafter. Reference is made to the accom- 1o panying drawing in which Figs. 1 and 4 represent a three-color filter provided with a mask allowing concentrically obturation;

Fig. 2 represents the same arrangement as Fig. 1; but the mask having a shape that in spite of the obturation the optical centre of gravity remains in the centre of the red and blue strips;

Fig. 3 shows a multi-coior filter in which noteworthy diflerences in the proportion of the areas so 02 each color occuronly when the filter is obturated so that a three-color filter remains which bears a mask of the shape shown in Fig. 1, and Fig. 4 shows a three-color filter with a blue,

a green and a red strip provided with a mask 25 before the green filter strip of which the curves uniting the cut-outs have been determined mathematically.

In taking moving pictures in natural colors according to the known Berthon process a multicolor-filter is used which consists'of several parallel areas of different colors, in the form of parallel strips. In this case the customary concentric reduction of the diaphragm aperture by means of circular or iris diaphragms cannot be applied, because as the step is increased the relatlve proportion of the areas of the color strips would be altered more and more in favor of the middle color strip, and it would therefore be impossible to obtain a picture in true colors.v

4 The present invention provides a parallel band multi-color filter which is capable oi being obturated cdncentrically, without leading to the production of colors which are not'the true colors. For this purpose there is fitted either in front of or on the filter a mask having a formsuch that the relative proportion oi the eflective color areas on the filter will not be altered by concentric stopping, whatever-be the size of the stop.

a Intheaccom drawinsl imlrcpresents,

N. Y., a corporation of New York 1935, Serial No. 2!,843 hjn'rchlL 1931 dclaim. (01. 95-815) by way of example, a mask o f the kind above described fitted on the middle portion of the filter and having an outline oi a determined shape. 1

When. the diaphragm of the objective (diam- 5 eter DiDi) is fully open, the eifective blue area of the filter consists of the zones in and b2, theeflective green area consists of the zones 01, as, as, and g4 and the effective red area consists of the zones n and ra.

When the objective diameter DzDs, I I

The blue area consists of the zone in, v The green area consists of the zones 02 and 0:.

The red areaconsists of the zone T2. The following equation must therefore be sat- The curves can be determined mathematically .cr empirically. when proceeding according to the empirical method, the-outline of the multicclor filter, for instance, of a three-color filter is drawn on a paper ruled in millimeters. To the circular outline of the filter there are drawn concentric circles. Then. the area of the middle filter strip between two adjacent concentric circles is subdivided symmetrically to the middle line of the middle filter strip so that the ratio of the sum of the partial areas oi the middle filter strips and the partial areas of the lateral filter strips remains the same. By uniting the corresponding points of the partial areas of the middle filter strip there are formed two curves which give the outline of the mask which is to be placed on the middle filter strip so that in concentric stopping the ratio of the diflerent colors remains always the same. q

If in Fig: 4 a designates half of the breadth of the middle filter strip, 1' designates the distance of a point of the curve from the center at the filter, or designates the angle between the middle line of the green filter "strip and 'r, and t the. angle between a point where one ofthe concentric circles to the outline of'the filter cuts the border-oi the green filter area and the perpendicular to this border line through the'center of the filter the following may be derived 10 has been obturated to the I Col- What I claim is:

A striped three-color filter for use with lenticg5 ular films of which the middle filter strip is provided with a removable m'ask havingoat the upper and the lower ends a cut-out of which the limiting curve is determined by the equationc.

k designating the ratio between the green and the sum or the red and blue filter areas,

a designating half or the breadth of the middle 111mstrip, r designating the distance of a point of the curve from the center 01' the filter,

p designating the angle between the middle line of a green filter strip and r, and

1p designating the angle between a point where go one of the concentric circles of the outline of the filter cuts the border of the green filter area and the perpendicular to this border line through the center of the filter.

01mm m 25 

